Means for synchronizing rotary devices



June 1o, 1930. A. D. Down 1,762,963

MEANS FOR SYNCHRONIZINGl ROTARY'DEVICES Filed April 26,l 1928 3ySheets-Sheet 1 June 10, 1930.

A. D. ADOWD l MEANS FOR SYNCHRONIZING ROTARY DEVICES Filed April 26,1928 5 Sheets-Sheet 2 Arm/Mfr lJune 10, 1930. -A. D. DowD MEANS FORSYNCHRONIZING ROTARY DEVICES 3 sheets-sheet s Filed April 26. 1928 .www5

Arron/vir ANDREW D. DOWD, OF .'HOBOXEN', NEW 'I'FRSIEIY,v ASSIGNOR TO'WESTERN ELECTRIC Patented .lune l0, 1930 UNITED STAT-Es PATENT OFFICECOMPANY, INCORPORATED, OF NEW YORK,v N-i .A CORPORATION OIF NEW YORKMEANS FOB vSYNCH'RONJZZING ROTARY-DEVICES Application led April 26,1928, Serial 170.272,90), vsind in Great Britain October 31, 192?. I

Thisinvention relatesto means for-synchronizing a plurality of rotarymembers and is particularly intended and adapted for use in so-calledsynchronous ltelegraph or signaling systems though alsov applicable forother apparatus, as for-example, thesynchronizing of picturetransmitting' apparatus. i

An object-of the invention is to maintain in -synchronism rotarydistributors at .terminal stations in a simplex telegraph system havingan intermediate station arranged to repeat signals in oppositedirections on long submarine cables.

A more speciiicobject of the invention is to automatically correct inboth forward and backward directions the speed of the dis-l tributors atthe repeatingand the receiving stations during each receiving intervalwhen such'distributors -pull out of phase with the l distributors at thesending station.

A preferred embodiment of 'the invention is shown and described hereinas being adaptable to a multiple-x printing submarine ca le telegraphsystem such as disclosed in U.S.

Patent No. 1,689,328 granted to A. M. Curtis* l on Oct. 30, 1928,l andtherefore a brief description of this system will( facilitatea clearunderstanding of the present invention. l In this system a number ofseparate printing telegraph transmitting and receiving mechanisms atboth ends of the'cable are connectedV in rotation so that eachtransmittingl circuit at one end is momentarily connected over the cableto its corresponding receivingcircuit at the other end. The amount oftime alotted to each circuit is equal to thetotal transmis-y sion timedivided by the number of separate sets of circuits. The cable operationis simplex, that is, messages are transmitted in one direction onlyduring a given interval of time and the direction of i transmission is lreversed automatically at statedintervals in order to' handle traiiic inbothf directions over one cable. In other words, .the transmissionmechanisms at one end of the able are con-4` nected to the receivingmech nisms at the opposite end of the cable forza ertainvperiod andthenreversed so that thai-transmitting mechanisms at the'oppositeondere-connected .beenset to the ldesired proportions of time.

The mechanisms for transmitting and receiving consist of' so-calledrotary distributors comprlslng 'transmitting rings, receivingringsandcorrecting rings. vThe correcting rings, whlch are .mounted oneach of the `senderv distributors, are arranged to be orientable -inrelation to the other rings on -,theirrespective distributors wherebythe system may be adjusted before the actual transmission of messagesbegins to establish synvchronism between the vsender distributor at oneend of the .cable and the receivingvdistributor yat the other end whensuch distributors` are interconnected for the transmission of messages.`In this manner, differentl amounts of time lag due to the transmissioncharacteristic of the cable may be compensated. The distributors have atendency to drift out of synchronism and phase during the intervals whenthe reversals of direction and transmission take place. Means for cor-.to the receiving mechanisms at the origin'atrecting this loss ofsynchronism and phase are disclosed in detailin U.. Si'Patent'No.

1,670,461, issued to G. A. Locke-on M ay 22,

1928, whichmeans are particularly adapted t'o systems-*having lonly twostations .inter- -correction is generally made in a forward direction,that is, in the direction .of-rotation of the distributor brushes and,.if it shouldbe desirable at any time to eil'ectgthe correction in. abackward direction, aman.- ually operatedtwo-position switch which is".provided for this ,purpose must be operated to its alternate positioninorder to shift the correcting ap aratus for backward movement of thed1stributor brushes.

I According to the present invention, correcting means somewhat, similarto those disclosed in the Locke patent, supra, are employed forrestoring synchronism and phase 1n a system in which two terminalstations and an intermediate station are interconnect- 1 ed by-a longsubmarine cable, but the proposed method of correcting rovides forcorterminal station and the intermediate sta-Q tion fall out ofsynchronism and phase with the distributor at the sending terminalstation, the correction can be applied at the receiving terminal stationand the intermediate station practically simultaneously.

This invention will be better understood by reference to the followingdetailed description taken in connection with the accompanying drawingin which Figs. 1 and 2 represent a diagrammatic layout of a multiplexsubmarine cable telegraph system which includes an inland terminalstation A, a land line, a shore te'rminal station B, a submarine cable,an intermediate, or repeater, station C, another submarinev cable, andanother terminalstation D, all connected in series. Fig. 3 shows thecorrecting mechanism used in connection with the apparatus at theterminal station D. f f

Inasmuch as the invention relates principally to a method and means `formalntaining in synchronism and phase the distributors at thc variousstations, such parts of the system as are not directly concerned withthe problem, for example, such apparatus as the transmitting andreceiving distributors, impulse transmitting and printin devices,driving motors, storing relays, an amplifier units: are merely indicatedby enclosures, while of the direction of transmission control apparatus,only the cams and spring contacts essential for the switching of theline for transmission in one direction or the other have been indicated.C n the other hand, the

lst

speed correcting or synchronizing means at the terminal station D have'beenshown in considerable dctailand this will be taken as beingrepresentative of similar means used inconnection with the receiving euipment at stations A and C. For a full understanding of the system,reference can be made to the Curtis patent, supra, as the followingdescription will be confined principally to such portions of the systemas are connected with the synchronizingproblem.

` Referring to Fig. -1 there is shown at the inland terminal station A,a transmitting distributor 100 with its associated impulse transmittingdevice 101 and a receiving distributor .102 with its printing device 103connect- Aed to contacts actuated by cam 104, which valternately connectsaid distributors to a land line.105. which extends to the shore'terminal station B. Correcting rings 106 with their associatedcorrecting apparatus 107 `are shown connected to the contacts of atwoposition correction control relay 108 at sta- -tion B. Relay 108 isshownconnected in series with the line relay 109 in the output ofamplifier 110 the latter being connected to the submarine cable 111whlch extends to the repeater station C.

` The equipment at station B comprises av receiving distributor 112 andits associated storing relays 113 from which the signals arevretransmitted through the transmitting distributor 114 to the submarinecable 111. Of

the direction control apparatus vat this station, only transfer relay115 and the cams 116 and 117 for controlling contacts )zo switch fromreception to transmission, and vice versa, have been shown. VAt thisstation, signals received from line y105 are repeated to cable 111through the receiving distributor 112, storing relays 113, transmittingdistributor 114, while the signals from the cable 111 are amplifiedthrough the amplilier 110 ,tovactuate line relay 109 whichdirectlycontrols the lretransmission of signals to the land line 105 through thecontacts actuated by cam- 116.

The corrector control relay 108 responds to they signals `incoming fromcable 111 and thereby causes the necessary correction in the receivingdistributor 102 through the correcting rings 106 and correctingapparatus 107. The correcting rings 106 are mounted on the sendingdistributor 100, and the correcting apparatus 107, which is forproducing angular shiftsof the brushes traveling overthe faces of thedistributors 100and 102,

is located between the motor (not shown). for driving the distributorsand the distributors themselves, as will hereinafter be explained. Thedistributors at station B are driven in synchronism with thedistributors of vstation A by mea-ns of the distributor arrangement 118at station A whereby impulses are sent over a separate line 119 to thedriving motor arrangement 120 at station B. .These arrangements areshown and described in detail in the Curtis patent, supra. No4correcting rings or apparatus are required for station B because` thedistributor thereat is driven from the same source as the distributor atstation A.

The submarine cable 111. terminates at repeater station C at which theequipment for receiving signals-includes an amplifying device 200, linerelay 201, receiving distribupeated to the correcting rings 207 for thefoperation vof the correcting apparatus 208 to.

rection control relay206 is in series"withthe line relay 201- andcontrols the impulses vreelfect the necessary. correction in the dis--tributors 202 and 204. Repeating signals in the o posite direction, thatis, from station D to i; through station C is accomplished by transferrelay 209 and cam 210 and transfer.

relay 211 and cam 212, all of which are under the control of thedirection control apparatus (not shown) cable 205 are received andamplified .by the amplifying device 213 and li'ne relay 214.'

Relay 214 repeats the amplified signals to receiving distributor 215 andstoring relays 216 and these repeated signals are retransmitted throughsending distributor 217 over cable 111 and land line 105, to'station'.The correction lcontrol relay 218 is in series with the line relay 214to control the impulses repeated to the correcting rings 219 foroperating correcting apparatus 220. to effect the necessary correction`in the distributors 215 and 217. Two sets of distributors with separatecorrecting apparatus are provided at station C to handle traic in bothdirections, the correcting-apparatus'208 being located between the motor(not shown) for driving distributors 202 and 204 and the distributorsthemselves, and the correcting apparatus 220 being located betweenthemotor (not shown),- 'for' driving ,distributors 215 and 217 and thedistributors themselves. .4 The correcting rings 207 and 219 arerespectively mounted on the sender distributors 204 aud`217.

' Submarine cable 205 terminates at station- D `at which the equipmentfor receiving signals consists of an amplifying device 221, linerelay`222, receiving-distributor 223 and the printing apparatus 224. Thecorrection con-v trol relay 225 is in series with the line relay 222tocontrol the correcting apparatus 226 through correcting rings 227.Transmission from station D is directed by-impulse trans'- mittingdevices 228 through the sending distributor 229 to cable'205 and thedirectionv control cam 230 causes throu h the operation offtransferrelay 231, the shifting of opera- `tion over the cable 205 from thereceiving to thef sending apparatus, and vice versa.

f The correcting apparatus 226v and correct- Fig. 3 and respectivelydesignated therein by ing rings 227 in Fig. 2 are shown in detail incharacters 326 and 327. The correcting rings are made up of acontinuousring and a segmented ring, the latter ring consisting ef tensegments for each channel employed in the f system.- For example,inafive-channel system such as described in the Curtis patent, supra,

the segmented ring consists of fifty segments.

' tures-of thls invention, a description will now be made of the vmethodof bringing the dis-v These iugs are interconnected by a rotatablebrush' 332 which, as 'it passes over each segment is arranged tocomplete a circuit for operating an auxiliary correction relay 333.

The signals incoming from diiferentlal beveled gear' arrangement 337`posite directions.

i 'f Relay 333 is al three-position relayand controls the'operation ofacorrecting mechanism 334. This mechanism is located between the motor(not shown) for driving the distribu. tors 323 and 329 andthedistributors themselves. The shaft'335 is driven by themotor -and theshaft 336 drives the arms on whichthe brushes, such as 332, for`thedistributors aremounted. These armsiare arranged to drive thebrushes over the various distributor faces in a manner well known in theart.'

he correcting'mechanism 334 consists of a disposed between the motorshaft 335 and the brush shaft 336 and the gears that link these twoShafts together are mounted on a supporting frame 338 secured to a wormpinion 339 that meshes with a worm 340. Any

change in the angular position -of the worm.

pinion 339 changes the angular osition of the linking gears and this inturn c anges the vangular posltion of the brush shaft 336 with respectto the motor shaft 335. The worm 340 is rotatable to shift the angularposition of the worm pinion a small angle by means ofcorrector magnets341 and 342 in one-direction or t-he other. The ratchet wheel and pawlmechanisms 343 and 344, respectively,

. TRAB- are operated by these magnets so that upon the operation ofeither one of the magnets, an angular shift of the distributor brushesin onedirection or the other is effective.A In

order to hold the worin 340 firmly while the magnets are not rotatingit, a separate-ratchet wheel 345 and a pawl 346 is provided. This wheeland pawl alsolimits the movement'o'f theworm 340 to one step each time acorrector magnet operates.v The automatic corrector mechanism 334 istherefore camhla 'nf Shin;-

tion of rotation of the brushes. It is seen,

therefore, that this mechanism corrects in either direction and can beeective while the distributor brushes are being rotated by the motor andin this way synchronizing effects maybe produced between the brushes ofthe distributors at thediff'erent stations, as will hereinafterbem'ojlfef fully explained. The i automatic correctin'ggapparatus atstations A and C are identical with that shown in Fig. 3,

two sets being provided for station C in order to correct for.synchronism and phase in op- To more fullyset lforth the' various' fea-12oA l tributors at the various stations into synchro'- at stations B, Cand D may be regulated in` accordance with the determined speed of thedistributor at station A. That is to say, the fundamental speed will beset at station A although it should be remembered that during thetransmission of messages the station from which transmission takes placeat any given time sets-the pace at which the receiving stationdistributors will opera-te. As previously mentioned,the speed of thedistributor at `station B is controlled by the distributor drive rings118 at station A and will not be described herein in detail as theirarrangement is well known'in the art. `It is sluiicient to say that thespeed of the motor fordriving the distributors at station B lis entirelycontrolled from the impulses received over the line 119. If, therefore,the' distributors of station Aare setto a certain speed and the motoratstation B is regulated so that the distributors at station B aretraveling at the same speed, the next step will. be to vtransmitso-called phasing signals from the sending distributor 100 over line 105to the receiving distributor 112 at sta' tion B. The brushes of thereceiving distributor 112 must now be set in phase with the 'brushes ofthe sending distributor v100 at station A. This is done by means shownanddescribed in detail in thelCurtis patent,y supra, and is described ingeneralin the Locke. patent, supra. When this phase relation isattained, the signals received from station A are permitted to beretransmitted through storing relays`113 and the sending distributor 114over the submarine cable 111 to. station C. TheseV retransmitted signalsare now used by the operator at station C for determining the speed atwhich the distributors at station C shall travel and, as.

far as transmission `of signals between stations A and'C are concernedthe presence of\station B ma be disregarded in the following descriptionof the method of. synchronizing.

The operator at station C now proceeds in a manner similar to that ofthe operatory at station'B is phasing the brushes of the receivingdistributor 202 and, when this phase relation has been obtained, thecorrecting apparatus 208 is switched in to be cont-rolled by theimpulses produced Aby the corrector control relay 206. rlhe correctingapparatus will function to automatically correct the positions of thedistributor brushes in both for-v ward and backward direct-ions for anyloss of synchronism or phase occurring thereafter.

The signalsl received at station C are retransmitted through storingrelays 203, sending. distributor 204 over su marine cable 205 to stationD. These signals are used by the operator at station D for determiningthe speed at whichthe distributors at station D shall travel. Theoperator at station D also proceeds in a manner similar to that oftheoperator at station B and, when the brushes of the receivin distributor223 are broughtinto phase wit the brushes of sending distributor 204 atstation C, the operator at station D switches in the correctingapparatus 226 to 'be controlled by the impulses produced at thecorrection control relay 225 in response to the incoming signals.Correcting apparatus 226 will likewise function to automatically correctthe positions of thel distributor brushes at station D in both forwardand backward directions forlany loss of synchronism or phase.

In order to reverse the direction of transmission and reception so thatmessages may be transmitted from station D, the direction control cams104, 116, 117, 210, 212 and 2 30 are actuated -by a timing device (notshown). This timing device is merely a means for actuating the abovementioned cams at certain intervals to make'them perform thisdesiredswitching of the circuits atpredeterminedj -close the connectionsbetween the receiving distributor 102 and the line 105. Similarly, 'cam116 opens the connections between the receivingdistributor 112 and line105 and closes connections between line 105 andthe armature of linerelay 109.1l The cam 117 closes a circuit for the operation'of relay 115to open the connection between the submariney cable 111 and the sendingdistributor 114 andto close. a connection between this cable and theamplifying device 110. Signals incoming 4over cable 111 will thereforenow passas previously stated through the amplifyingdevice 110, linerelay 109 and correction control relay 109. The operation of cam 210closes a circuit for the operation of transfer relay 209 to causethis-relay to'actuate its armature to a position opposite to that shownin the drawing, thereby opening the connection between cable 111 and theamplifying device 200 and closing a connection between the cable and thesending distributor 217 .f Cam- 212, upon operating, lcloses a circuitfor the operationof transfer relay 211l to cause this relay to open theconnection between the cable 205 and the sending distribu-v tor 204 andto close a connection between the cable and amplifying device 213 atwhich de- 15. tion C, B and A to the speed of the distribuand storingrelays 216 for retransmission stations C and B to station A may nowbegin vses through sending distributor 217. The operation of cam 230operates transfer relay 231 to open the connection' between cable 205and receiving apparatus at station D and to close a connection betweenthe cable andthe sending distributor 229.

When the operations of the aforementioned cams are completed, thetransmission of phasing signals from station D through repeaterfor-'synchronizingof the distributors at stator at station D. It will berecalled that the arrangement of the system is such that the sendingstation is a pace-setting .station -although the distributors at allfour stations are operating at the one speed..v When the phasing isaccomplished at each station in turn, the ,correcting apparatus at there eating station C and the receiving station are connected formaintaining the distributors at their respective stations insynclironism and phase.

lF ig. 3 shows the equipment at -station D more in detail than Fig. 2,different characters heilig used for corresponding elements to avoidconfusion in referring to the two figures. The correcting rings 327 areshown connected through the continuous, or upper, ring to the ,contactsof the correction control relay 325. Relay 325 is atWo-positionpolarized relay having an armature arranged to remain iii4 one positionwhile signals of one polarity arebeing received and to move to itsalternate position when the polarity of the signals is reversed. Thesegmented ring of ring set 327 is arranged in two groups of alternatesegments, vone group A being connected in a circuit extending throughthe left-hand winding of auxiliary correction relay 333 and the othergroup R connected ina circuit extending through the right-hand windingof relay 333. Relay 333 is a threeposition polarized relay having anarmature arranged to be normally in a neutral position tributors '229and 223 in Fig. 2 in either av but effective to engageeither of twoassociated contactsl in response to a current flowing through either ofthe above mentioned windings. When the armature of relayV 3331engageseither of its associated contacts, one or the other of the correctormagnets 341and 342 operates to move the brushes on the disforward or abackward direction, the direction depending on whic vwindin of relay 333is energized. When rotatable rush 332, .which interconnects the rings ofring set 327, 1s in contact with an A segment at the instant relay 325moves from one contact to the other,

the left-hand winding oferelay 333 becomes energized, operatingcorrector magnet 341 to 'handwinding of relay 333 to negative move thebrushes in a forward direction and when the brush is in contact vwith anR segment the right-hand winding of relay 333 becomes-energized and themagnet 342 opcrates` to move the brushes in a backward brush correctionis in a forward or a backward-direction-according as the brush 332 is incontact with an A (advance) or R (retard) segment; and if, as will bethe case if. the distributors'of station D are in perfect phase relationwith the distributors of station C, the brush 332 is passing over one ofthe' insulated spaces between an A and an R segment at the instant oftheactuation of relay 325, no circuit Will be completed to either of thewindings of relay 333. Assuming that the brushes of the distributor ofstation D are lagging behind the brushes of the distriby utor at stationC taking iinto consideration the characteristic lag of the cable 305,brush 332 will be' in contact with an A segment as shown instead of incontact -with the insulated space following it, and a circuit` istherefore closed, traceable from positive battery 347, armature andright-hand contact of relay 325, condenser 348 and high resistance 349in parallel, conductor 350, continuous ring, brush 332, andan segment ofring set 327, conductor 351, back contact and armature of magnet 341,conductor 352, left-hand winding of relay 333,*t'o negative battery 353,

direction. It will be seen, therefore, that the but not enoughcurrentwill flow in this circuit at this time because of the highresistance in parallel to the condenser 348. At the next reversal ofpolarity of the incoming signals, the armature of relay 325 moves to itsalternate position and closes a circuit extendingfrom the positivebattery 347, armature and left-hand contact of relay 325, condenser 354and high resistance 355 in parallel, conductor 350 over the same pathjust traced-to the negative battery 353. A surge of current is producedin the circuit including condenser 354 at the moment the armature and-left- 343 to shift, through the corrector mechanism 326, the'sh'aft 336for a small angular distance in a forwarddirection in relation to therotation of the shaft. This shifting of shaft 336 causes the brushes ofthe receiving distributor 323 and brush332 of the correcting rings 327to move forward a correspondingangular distance. When relay 333operates,

it closes'at its left contact and armature` a 1 locking circuit foritself extending over con'- ductor 357, resistance 358, through theleftbatl tery 353, and this locking circuit prevents the release of therelay until magnet 341 has reached its fully operated position. Whenmagnet 341 reachesits fully operated position, a circuit is closedextending from positive battery 356, armature and left contact of relay333, conductor 357, resistance 358, armature 'and front contact ofmagnet 341, conductor 359, to negative battery 3 53, and this circuitshunts the left-hand winding of relay 333 which now releases itsarmature, thereby causing the release of magnet y.341. In this mannerrelay'333 is prevented from operating 'in response to another ,impulsereceived from the correcting rings unt-il the magnet 341 is fullyrestored to its normal position. At

l the next reversal of polarity of' the incoming signals passing throughthe windings of relay 325, a brush will again be in contact with an Asegment if synchronism or phase has not been restored, and the relayarmature will move toits right-hand Contact to send another-impulse frompositive battery 347 through the left-hand Winding of relay k333. Relayv333Willl again operate and cause the correcting mechanism 336 to movethe distributor brushes another step in a forward direction. `Resistance358 is of a value such that the holding current passing therethrough andthrough the left-hand winding o--relay 333 is not suiiicient to preventthe release of the reposition, to operate corrector magnet 342 overYThus,` animpulse of positive current is sent on each reversal throughthe condensers 348 and 354 alternately and through an R segment,providing relay 333 is in its normal a circuit extendingfrom positivebattery 347,

y through either condenser 348 or 364 and an R segment, backl contactand armature of magnet 342, conductor 360, through the righthand windingof relay 333 to negative bat tery 353. vRelay 333 operates andinterconnects its armature and right-hand contact to close a circuitextending from positive battery 356, armature and right contact of therelay, conductor 361, through the winding of magnet 342 to negativebattery. Magnet 342 eoperates 'and actuates the pawl and 'ratchetmechanism 344 to shift the shaft 336 for a small angular distance in abackward direction in relation to thel rotation of the shaft. This shiftofthe shaft causes the brushes of the receiving distributor 323 andbrush 332 of the correcting ring 337 to move backward a correspondingangular distance.

impulses from positive battery 347 until magnet 342 hasbeen restoredtoits normal position. `The resistance 362 is the same value asresistance 358 and the holding current passing therethrough and theleft-hand winding of relay 333 is not suflicient to prevent the releaseof the relay when the armature of magnet 342 engages the front contactof the relay. i

Inasmuch as the correcting apparatus at stations A and C areliden'ticalwith that shown in Fig. 3, their operations. will be the same as thosefor the apparatus at station D. No further description will benecessary. By this method of correction the motors at all the stationsin the system may be operated at the one speed, and for any loss ofsynchronism or phase which may occur in the intervals at reversals intransmission to reception and vice versa, when no impulses are beingtransmitted, the correcting mechanisms at the receiving stations mayautomatically shift the brushes of their respectivelyassociateddistributors in-both forward and backward directions during eachreceiving interval.

What is claimed is:

1. .In a synchronous telegraph system,a transmission -line,.distributorsand brushes therefor connected to opposite ends of said line;synchronizing means for said distributors controlled by the distributorat the sending end of' said line, means for stepping the brushes aroundthe distributor at the receiving end `in both forward and backwarddirections withrespect to the direction of tributors and rotatingbrushes therefor arrangedto operate at the one speed, a transmissionline interconnecting said stations,

-means for automatically reversing the direction ofptransmission fromtime to time, lsyn-l chronizing means at each of said stationscomprising a plurality of correcting clock- '1'otation, automatic' meansfor eiecting the change of brush stepping from one direction handmechanisms for stepping the .distribu-.

tor-brushes in bothforward and backward directions with respect to the'direction of rotation,in response to the current reversals of theincoming signals should the distributors at the receiving stations pullout of phase with the distributor at the sending station and automaticmeans for reversing the brush stepping operation should the brush bestepped beyond its desired phase.

3. In a synchronous telegraph system, a transmission line, a rotarydistributor comprising a continuons and a segmented ring and associatedwith said line, a rotatable brush interconnecting said rings, twoelectri cally controlled clockhand mechanisms for stepping -said br-ushin responseI to reversals of current of the incoming signals in forwardand backward directions with respect to the direction of rotation whileit is rotating, to vary the speed of sai/d brush in accordance with thespeed of the incoming signals, autolnatic means .for changing thedirection of said stepping operation and means for pre-4 venting thefurther operation of either mecl1` anism until such mechanism ispositively restored to its normal position.

4. In a synchronous telegraph system, a transmisison line adapted forsimplex operation, a rotary distributor comprising a continuous anda-segmented ring associated with said line, a rotatable brushinterconnecting said rings, two electrically controlled clockhandmechanisms for automatically stepping said brush in response toreversals of current of the incoming signals, in both forward andbackward directions with respect to the direction of rotation `While itis rotating, to Vary the speed ot' said brush in accordance with thespeed of the incoming signals, a twopo .sition relay in series with saidline andresponsive to current reversals of the incoming signals, athree-position relay for operating either of said mechanisms. a circuitfor operating the second mentioned relay should said brush be out ofphase with the incoming signals, and means in said circuit forpreventing the reopcration of said second relay until said mechanismsare fully restored to their normal positions.

In witness whereof, I hereunto subscribe my name this 25th day of AprilA. D., 1928.

ANDREW D. DOWD.

